The invention relates to the field of medical devices, and more particularly to catheters, such as needle catheters or other elongated devices configured for inserting into a patient's body lumen or cavity to perform a diagnostic and/or therapeutic procedure.
During a treatment or diagnostic procedure using an interventional catheter slidably disposed in a patient's coronary or peripheral vasculature, it may be necessary to rotate the catheter to properly position an operative distal end component in a specific rotational orientation relative to the treatment location in the patient's anatomy. For example, in a drug delivery procedure using a needle catheter, the ability to rotate the distal tip of the catheter would facilitate performing injections at multiple adjacent locations to more fully treat an area of the patient's anatomy. Typically, the physician attempts to orient the distal end of the catheter inside the patient by rotating the proximal end of the catheter outside the patient. However, in the construction of elongated intravascular catheters, one difficultly has been the tendency of the catheter shaft to exhibit wind-up and whipping in the anatomy, which makes it difficult to accurately orient the operative distal end at equally spaced rotational intervals by rotating the proximal end of the catheter.
As the physician rotates the proximal end of the catheter during a procedure, at the start of rotation, friction on the device outer diameter and energy loss due to dampening (and overcoming any curve preset in the shaft) requires that a torque and an amount of rotation be applied to the proximal end of the shaft before the distal portion begins to rotate. In other words, some amount of energy is stored in the shaft and some amount of energy is converted to heat prior to its distal portion beginning to rotate. This rotation required to overcome friction and damping is called wind-up. During rotation, as the amount of stored energy in the shaft increases, this extra required energy is obtained by reducing the amount of the rotation of the distal end of the shaft relative to the proximal end, causing an increased proximal applied torque. Conversely, during rotation, as the amount of stored energy in the shaft decreases, this released energy causes the amount of the rotation of the distal end of the shaft relative to the proximal end to increase, causing a decreased proximal applied torque. When the proximal end of the shaft is rotated at a constant rate, the distal end of the shaft will tend to remain at or near (rotate slowly at) rotational orientations with minimum stored energy, rotate rapidly when approaching the rotational orientations where the shaft stores a minimum amount of energy relative to adjacent orientations, rotate slowly when approaching the rotational orientations where the shaft stores a maximum amount of energy relative to adjacent orientations, and to rapidly rotate or jump past the orientations with a maximum energy storage. This is called whipping.
The physical basis of whipping is the variation with rotational orientation of the flexural modulus or bending moment of the catheter shaft when it is confined in a curved conduit such as the patient's aortic arch or other curved anatomy, or a curved section of a guide catheter. This causes the amount of stored energy in the shaft to vary with rotational angle in a shaft portion that is rotated while it is confined in the curved conduit, thus producing the maximum and minimum energy storage rotational orientations that result in the whipping. Because unintentionally induced whipping can make it very difficult or impossible to adequately control the distal rotational orientation of the device by rotating the proximal end, a design objective in many conventional percutanteous catheters, especially where rotational orientation control is desired, is to minimize whipping. A variety of features and conditions are considered in the design of catheter shafts to minimize whipping. In general, all other factors being equal, the least whipping and wind-up occurs in shafts with the highest torsion modulus to flexural modulus ratio. Additionally, designing and processing a shaft (i.e., the entire length of the shaft or just a section thereof) to have a consistent flexural modulus/bending moment as it is rotated regardless of the rotational orientation of a bend applied to the shaft, and avoiding setting a bend in the shaft, will minimize whipping. However, a consistent flexural modulus may require features such as consistent wall thickness, consistent/linear elastic material properties, the spiraling of shaft components, and/or concentric shaft designs, which are most often not practical to include or obtain.
With catheters having a pre-set bend formed in the shaft, the bending moment and energy storage of the catheter shaft is minimized when the pre-set bend of the catheter shaft portion aligns with a curve of a conduit such as the patient's vasculature or guiding catheter, and the catheter preferentially assumes this rotational orientation. However, this results in the catheter being limited to a single easily attained rotational orientation relative to the curved conduit, and is not useful when two or more catheter rotational orientations relative to the curved conduit, or a rotational increment of other than 360 degrees, are desired.
It would be a significant advance to provide catheters that allow for accurate control of the distal rotational orientation of the device by rotating the proximal end.